mybatis实现一对多连接查询

 

问题：两个对象User和Score，它们之间的关系为一对多。 

底层数据库为postgresql，ORM框架为mybatis。 

关键代码如下： 


mybatis配置文件如下： 

mybatis.xml文件内容为： 

 <?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
    PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <settings>
        <setting name="cacheEnabled" value="true" />
        <setting name="lazyLoadingEnabled" value="true" />
        <setting name="multipleResultSetsEnabled" value="true" />
        <setting name="useColumnLabel" value="true" />
        <setting name="useGeneratedKeys" value="true" />
        <setting name="defaultExecutorType" value="SIMPLE" />
        <setting name="defaultStatementTimeout" value="25000" />
    </settings>
    <typeAliases>
        <typeAlias type="com.mybatis.domain.User" alias="User" />
        <typeAlias type="com.mybatis.domain.Score" alias="Score" />
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="org.postgresql.Driver" />
                <property name="url" value="jdbc:postgresql://localhost:5432/mybatis" />
                <property name="username" value="postgres" />
                <property name="password" value="admin" />
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="com/mybatis/domain/User.xml" />
        <mapper resource="com/mybatis/domain/Score.xml" />
    </mappers>
</configuration>

User.java代码为： 

package com.mybatis.domain;

public class User {

    private Integer id;//用户id

    private String username;//用户名

    private String password;//密码

    private String address;//地址

    public User(){

    }

    public User(String username,String password,String address){
        this.username = username;
        this.password = password;
        this.address =address;
    }

    public User(Integer id,String username,String password,String address){
        this.id = id;
        this.username = username;
        this.password = password;
        this.address =address;
    }

    public int getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String toString(){
        return "当前用户为：id = "+id+",username = "+username+",password = "+password+",address = "+address;
    }

}

Score.java代码如下： 

 package com.mybatis.domain;

public class Score {

    private Integer id ;//主键id

    private User user;//所属用户

    private int math ;//数学成绩

    private int chinese ;//语文成绩

    private int english ;//英语成绩

    private int computer ;//计算机成绩

    public Score(){

    }

    public Score(User user, int math,int chinese,int english,int computer){
        this.user = user;
        this.math = math;
        this.chinese = chinese;
        this.english = english;
        this.computer = computer;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    public int getMath() {
        return math;
    }

    public void setMath(int math) {
        this.math = math;
    }

    public int getChinese() {
        return chinese;
    }

    public void setChinese(int chinese) {
        this.chinese = chinese;
    }

    public int getEnglish() {
        return english;
    }

    public void setEnglish(int english) {
        this.english = english;
    }

    public int getComputer() {
        return computer;
    }

    public void setComputer(int computer) {
        this.computer = computer;
    }

    public String toString(){
        return "id = "+ this.id+",math = "+this.math+",chinese = "+this.chinese+",english = "+this.english+",computer = "+this.computer+
                ", userid = "+this.user.getId()+",username = "+this.user.getUsername()+",password = "+this.user.getPassword()+
                ",address = "+this.user.getAddress();
    }

}

user.xml中的关键代码为： 

<resultMap type="User" id="userResult">
  <id property="id" column="userid"/>
  <result property="username" column="username"/>
  <result property="password" column="password"/>
  <result property="address" column="address"/>
</resultMap>

这里的对象的属性id对应的数据库表列名为userid，这是user对象为pg_score表中 

的标示。 

score.xml代码如下： 

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="ScoreDaoMapping">
    <resultMap type="Score" id="score">
        <constructor>
            <idArg column="id" javaType="int" />
            <arg column="userid" javaType="int" />
            <arg column="math" javaType="int" />
            <arg column="chinese" javaType="int" />
            <arg column="english" javaType="int" />
            <arg column="computer" javaType="int" />
        </constructor>
    </resultMap>

    <resultMap id="joinSelectScore" type="Score" >
      <id property="id" column="id"/>
      <result property="math" column="math"/>
      <result property="chinese" column="chinese"/>
      <result property="english" column="english"/>
      <result property="computer" column="computer"/>
      <association property="user" column="userid" javaType="User" resultMap="UserDaoMapping.userResult"/>
    </resultMap>

    <insert id="insertScore" parameterType="Score">
       insert into pg_score(math,chinese,english,computer,userid) values(#{math},#{chinese},#{english},#{computer},#{user.id})
    </insert>

    <select id="findScoreByUser" resultMap="joinSelectScore" resultType="list" parameterType="map">
         select
                s.id as id,
                s.math as math,
                s.chinese as chinese,
                s.english as english,
                s.computer as computer,
                u.id as userid,
                u.username as username,
                u.password as password,
                u.address as address
         from pg_score s left outer join pg_userinfo u on s.userid = u.id where u.id=#{userid}
    </select>

</mapper>

ScoreDao.java中的关键代码为： 

private  String resource = "com/mybatis/configuration/mybatis.xml";
    public List<Score> selectScoreByUser(User user) throws IOException{
        Reader reader = Resources.getResourceAsReader(resource);
        SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(reader);
        SqlSession session = ssf.openSession();
        reader.close();
        Map<String,Integer> params = new HashMap<String,Integer>();
        params.put("userid", user.getId());
        List<Score> scoreList = session.selectList("ScoreDaoMapping.findScoreByUser", params);
        session.commit();
        session.close();
        return scoreList;
    }

ScoreService.java代码如下： 

package com.mybatis.service;

import java.io.IOException;
import java.util.List;

import com.mybatis.dao.ScoreDao;
import com.mybatis.domain.Score;
import com.mybatis.domain.User;

public class ScoreService {

    private ScoreDao scoreDao = new ScoreDao();

    public ScoreDao getScoreDao() {
        return scoreDao;
    }

    public void setScoreDao(ScoreDao scoreDao) {
        this.scoreDao = scoreDao;
    }

    public List<Score> getScoreByUser(User user) throws IOException{
        return scoreDao.selectScoreByUser(user);
    }

    public void insertScore(Score score) throws IOException{
        scoreDao.insert(score);
    }
}

Test.java代码如下： 

package com.mybatis.test;

import java.util.List;

import com.mybatis.domain.Score;
import com.mybatis.domain.User;
import com.mybatis.service.ScoreService;
import com.mybatis.service.UserService;

public class Test {

    private UserService userService = new UserService();

    private ScoreService scoreSerice = new ScoreService();

    public static void main(String[] args) throws Exception{

        Test test = new Test();
        //test.insertScore();
        List<Score> scoreList = test.getScore();
        Score score = null;
        for(int i=0;i<scoreList.size();i++){
            System.out.println("第"+(i+1)+"个score对象为：");
            score = scoreList.get(i);
            System.out.println(score);
        }

    }

    public void insertScore() throws Exception{
        List<User> userList = userService.getPageUsers(10, 0);
        User user = userList.get(2);

        Score score = new Score();
        score.setUser(user);
        score.setChinese(80);
        score.setComputer(90);
        score.setEnglish(91);
        score.setMath(98);
        scoreSerice.insertScore(score);
    }

    public List<Score> getScore() throws Exception{
        List<User> userList = userService.getPageUsers(10, 0);
        User user = userList.get(0);

        List<Score> scoreList = scoreSerice.getScoreByUser(user);
        return scoreList;
    }

/*  public User getUserById(int id) throws Exception{
        return userService.getUserById(id);
    }*/
}